Oracle optimizer estimation is way off. An insert statement runs forever even the execution plan sho

An insert statement is stuck at table scan on WSH_NEW_DELIVERIES table.

Even though xplain plan showed indexes are used and the estimated completion was very short, the insert statement is stuck at WSH_NEW_DELIVERIES (based on v$session_longops view) and had been running for more than 15 hours before I terminated the session.

Actions have been taken

1) Gathered the table's latest statistics on all relaited tables via dbms_stats

2) Ran Validate table WSH.WSH_NEW_DELIVERIES but no corrutption blocks reported in V$DATABASE_BLOCK_CORRUPTION table

3) WSH.WSH_NEW_DELIVERIES table information: 18,297,742 records and 93,184 blocks (730MB)